President Bush may have unwittingly done the stem cell research community a big favor in 2001 when he outlawed federal funding for all but a very limited category of work in the field.

For all that scientists bemoan Bush's ideologically inspired hobbling of a highly promising biomedical discipline, stem cell research has since acquired a gratifyingly high profile. Nancy Reagan and Ron Reagan Jr., believing that the new science might alleviate the Alzheimer's disease that afflicted Ronald Reagan in his last years, have urged Bush to reverse himself. Sen. John F. Kerry also has supported lifting the restrictions.

And now, here comes Proposition 71.

Scheduled for November's state ballot, Proposition 71 calls for a $3-billion bond to finance stem cell research in California. The initiative has been endorsed by business lobbies, medical associations and political leaders (mostly Democrats) who see California becoming the world's stem cell capital, with all that means in new business, employment and prestige.

"There's the possibility of putting California in the front ranks of biotechnology," says Treasurer Phil Angelides, who with Controller Steve Westly is the measure's biggest Democratic fan. "It's a risk worth taking."

But even if you accept that stem cell research may someday alleviate ailments such as diabetes and Lou Gehrig's disease, there's cause to wonder whether Proposition 71's sponsors aren't overselling the state of knowledge in the field — and understating the proposal's cost.

It may be hard for voters to fully grasp the vastness of this financial commitment. No research program approaching this scale has ever been mounted by any state. The effort, elephantine even by California standards, would allocate nearly twice as much money to one scientific field as the University of California has spent on all its research facilities over the last 25 years. It would dwarf the California Breast Cancer Research Program, the largest state-sponsored research effort in the nation, which has granted scientists a comparatively paltry total of $150 million since 1994.

Proposition 71's supporters contend that the program is appropriately sized, given the breadth of the undertaking.

"We're dealing with 70 different diseases, not one," says Robert Klein II, the Northern California real estate developer who is the measure's driving force.

Klein, who has a 14-year-old son with juvenile diabetes and a parent with Alzheimer's — and who has contributed $2 million of the $7 million raised by the stem cell campaign thus far — says researchers need the long-term financial support, insulated from budgetary fits and starts, that can be provided only by a big state bond.

Still, the sponsors have sugar-coated the program's real cost of $6 billion (including interest). They say the bond won't "increase or create any new taxes," but they can't back up that pledge.

New state income and sales taxes generated from the program will supposedly cover the interest due on the bonds during the first five years. But the supporters' own economic study shows that in the following nine years, when annual debt service on the bonds soars to more than $170 million, the putative tax gains will cover only 11% to 19% of that sum.

Where will they find the rest?

They say they're confident that millions of dollars will roll into state coffers from patent royalties, new businesses attracted by California's turbocharged research environment and healthcare savings derived from stem-cell-inspired cures.

But that's highly conjectural. UC's royalty revenue in 2003 from its entire portfolio of 900 patented inventions came to $67 million. As for when, or even whether, stem cell research will produce a healthcare bonanza, most leading researchers are loath to guess.

"There may be an unwarranted impression that widespread clinical application of new therapies is certain and imminent," a 2002 National Academy of Sciences report noted. "In fact, stem cell research is in its infancy." Barring a big jackpot, then, the stem cell bonds will be repaid out of the state budget — which is, um, financed by taxes.

Is the Proposition 71 campaign unrealistically raising people's hopes by glossing over the scientific challenges ahead? One has to dig mighty deep in the campaign website (named, prematurely, curesforcalifornia .com) to find any caveats about the current state of stem cell science.

Much more prominently featured is a stream of personal testimonials about the suffering caused by maladies that may (or may not) respond, someday, to stem cell therapy. Moving as these accounts are, to deploy them on behalf of a $3-billion state bond issue is simply an appeal to emotion.

That brings us to how the stem cell program fits into California's overall research picture. In part to avoid facing this question, the backers of Proposition 71 deliberately avoided bringing the issue to the state Legislature, which is responsible for weighing competing demands for state resources.

Klein says he didn't want the program "encumbered by lots of political considerations." Presumably, what his group really feared was the cumbersome process by which elected representatives decide whether, say, $3 billion in state debt capacity should all go to stem cell research or to a broader biomedical research program, or even to highway construction or schoolroom renovation instead. If Proposition 71 passes, such choices will be severely constrained.

And no one should forget that the Proposition 71 campaign is political anyway: It's the legacy of the philistine science policy of the White House, which has forestalled a national debate over the costs, possibilities and moral implications of stem cell research. One prominent stem cell expert and supporter of Proposition 71 described the initiative campaign as "a substitute for the national dialogue." But with a potential bill of $3 billion plus interest, this talk sure won't be cheap.